The aim of this research program is to define the role of oxidative stress as a signaling molecule for noise induced inner ear pathology and hearing loss and identify new interventions that may attenuate noise induced hearing loss (NIHL). Previous work has demonstrated the robust noise-induced formation of free radicals (both reactive oxygen and nitrogen species, ROS/RNS) and their distribution in the inner ear, in vivo, in the guinea pig. We have shown attenuation of NIHL with agents that prevent formation and scavenge free radicals or function at other sites of free radical-triggered apoptotic pathways (e.g., block apoptotic genes). Our research has also demonstrated a relationship between interventions that prevent free radical formation in the organ of Corti (but not lateral wall) and attenuation of NIHL. In addition we have defined a ROS dependent mechanism that underlies the long observed noise-induced reduction of local blood flow, with potentially damaging consequences. These previous findings now lead to the formulation of a model in which ROS and RNS are formed in the inner ear, during and following exposure to high levels of noise that trigger multiple biochemical pathways leading to cell death, with sites of intervention identified that can attenuate NIHL. This model forms the basis for the current program. In this continuation program we will assess the extent to which drug efficacy in prevention of NIHL is dependent on the interaction of factors that function at varied sites along the ROS-triggered paths. Our proposed studies will test hypotheses that efficacy of prevention is enhanced by synergy across agents. On the basis of most recent findings that ROS and particularly RNS form following a delay after noise exposure, suggesting that post-exposure treatment can attenuate NIHL, we will assess the efficacy of RNS and ROS scavengers administered following trauma to attenuate NIHL. Importantly, we will assess the extent to which survival vs apoptotic induced pathways are intensity dependent, and how this determines the transcription factors that effect cell survival following noise. We will also determine if reduced blood flow potentiates NIHL, in vivo. These studies will define new interventions and synergies at sites along the apoptotic pathway to optimize the prevention of NIHL.